1. Field of Invention
The present invention relates to a bonding pad having a large area contact surface providing for connection of an electrical energy storage device to an implantable medical device.
2. Prior Art
Implantable medical devices, such as pacemakers, require an electrical energy storage device as a power source that is easily connected to the device. Typically, the terminal leads of the power source are connected to the medical device directly by welding or soldering. The desire to wire bond directly from a medical device to a power source requires special processing of the terminal leads to prepare them for wire bonding. For example, the terminal leads must be flattened and plated with an applicable bonding media, i.e. gold. The flattening and plating process requires multiple operations that deviate from the normal process flow. Also, flattening a terminal lead does not necessarily assure that there is sufficient surface area to effect a robust connection. A cost-effective alternative is a bonding pad.
U.S. Pat. No. 4,371,231 to Jung, for example, is directed to an electrically conductive connection consisting of a very thin gold wire and a metal contact dot situated on an electrical component or on an integrated circuit. The contact dot includes a plurality of rectangular perforation holes contacted by the nailhead of the gold wire. The other end of the gold wire connects to an external terminal. The problem is that it is often unsuitable to directly bond the end of a wire to a contact surface because there is not enough bonding surface.
U.S. Pat. No. 3,418,422 to Bradham III describes an attachment for integrated circuit leads comprising a KOVAR lead electrolessly plated with nickel. Gold is then electrolessly plated over the nickel. The electroless gold and the electroless nickel form a solid solution type of alloy that normally has a minimum melting point of 950° C. The problem is that these multiple plating steps add considerable cost in terms of time and materials to the manufacturing process.
U.S. Pat. No. 5,116,700 to Takeda is similar to Bradham III, but is not intended for wire bonding or brazing. Instead it is directed to a soldering connection which is basically a flat lead used to connect a battery.